Secondary recovery of viscous crude oil



April 19, 1966 F. G. CRIDER SECONDARY RECOVERY OF VISCOUS CRUDE OIL Filed June 21, 1963 INVENTOR. FRETWELL G. CRIDER ATTORNEY United States Patent 3,246,693 SECONDARY RECQVERY 0F VISCGUS CRUDE OIL Fretwell G. Crider, Arlington, Tex., assignor to Socony Mobil Oil Company, Inc., a corporation of New York Filed June 21, 1963, Ser. No. 289,587 6 Claims. (Cl. 166-2) This invention relates to the secondary recovery of viscous crude oil from heavy oil subterranean reservoirs. More particularly, it relates to the recovery of viscous crude oil from oil-bearing formations by in situ combustion.

Vast amounts of viscous crude oil are disposed in heavy oil reservoirs. The amounts of such crude oil in place have been estimated to be in excess of 4 billion barrels. The crude oil is characterized by a low gravity and a hi h viscosity. For example, a typical viscous crude oil may have a 14 API gravity and a viscosity of about 600 centipoises at 100 F. The heavy oil reservoirs are usually characterized by a shallow depth, poorly consolidated sand and high-oil and low-gas saturation. The characteristics of the crude oil and the reservoir make the recovery of the low-gravity, viscous crude oils very dlfilClllt. As a result, only a small portion of the crude oil of this type has been recovered.

Many secondary recovery methods have been pro posed for recovering the low-gravity, viscous crude oil from heavy oil reservoirs. The most useful of these methods has been the in situ combustion procedure. The in situ combustion procedure is a thermal oil recovery method where the energy required for moving the crude oil through the reservoir and eventually into a production well is created by injecting air into the reservoir and in situ burning a portion of the crude oil. The procedure can be generally visualized as a slowly moving burning zone of narrow thickness which advances from the ignition well through the formation, moving the crude oil to the production well. By this means, the thermal energy from the burning zone is transferred to the crude oil by conduction through the sand and by convection through the reservoir fluids. The air may be injected from the ignition well to the production well so that the burning zone is moved by direct combustion. Alternatively, the air may be injected countercurrently to the movement of the burning zone so that the burning zone is advanced by inverse burning.

It will be apparent that many benefits arise from the in situ combustion procedure as a secondary recovery method for the low-gravity, viscous crude oil found in the heavy oil reservoir. One benefit is through the reduction of viscosity which occurs as a result of increased temperature in the reservoir. The markedly great effect of temperature on the viscosity and displacement on low-gravity, viscous crude oil demonstrates an inherent advantage of the thermal methods over the other secondary recovery methods which have been proposed for recovering such crude oil. F or example, a crude oil having a viscosity of about 600 centipoises at 100 F. is reduced to about 67 centipoises when the temperature of the oil is only raised from 100 F. to 175 F. Additional advantages in reduced viscosity and increased mobility of the crude oil occur through the thermal degradation, by cracking of the hydrocarbons and other means, from the burning zone passing through the reservoir. Thus, by a combination effect through in situ heating, the oil recovery efficiency of this secondary recovery method is greatly increased over other known procedures. The oil recovery efiiciency, as the term is used herein, includes both the rate and the ultimate amount of crude oil recovered from the reservoir.

3,240,693 Patented Apr. 19, 1966 The in situ combustion procedure utilizes a portion of the crude oil in the reservoir as a source of energy for producing the necessary heat energy to increase the temperature in the reservoir. In general, the heat of combustion of the crude oil may be assumed to be between about 16,000 and 19,000 B.t.u.s per pound. Obviously, only a small amount of the crude oil must be burned to produce the necessary heat to increase the temperature of the reservoir sufiiciently to produce the crude oil. This has .been proven by a field test in which a typical low-gravity, viscous crude oil was produced from a heavy oil reservoir and the amount of crude oil burned was only 15 percent of the total crude oil in the reservoir.

It has been found that in certain situations, the crude oil displaced before the burning zone cannot pass through the reservoir to the production well at a sufficient rate .to prevent accumulation of a liquid mass of crude oil immediately preceding the burning zone. Many instances have been encountered in which the liquid mass is of suflicient density that it is impossible to apply sufficient air fiux to maintain the burning zone. This may be commonly termed as the formation of a liquid block. It will be obvious that the displaced crude oil must move to the production well at a rate sufficient to permit the burning zone to advance. The burning zone must advance with at least a minimum rate sufiicient to receive an appropriate amount of air flux to sustain combustion. The air flux usually is not below about 1.2 standard cubic feet of air per hour per square foot of the burning zone. Usually, the minimum rate of burning zone advance in a heavy oil reservoir is about 0.12 foot per day. This is about the absolute minimum rate necessary to sustain combustion. It will be apparent that the characteristics of the low-gravity, viscous crude oil and the heavy oil reservoir may be such that a liquid block occurs even at this minimum rate of advance. When the liquid block occurs at the minimum rate of combustion advance, combustion ceases in the burning zone.

Usually it will be desirable to produce the crude oil at the highest possible rate of burning zone advance consistent with good operation procedures. It has been observed that the maximum rates of advancement of the the burning zone in field tests are about 3.0 feet per day where liquid blocks were not formed. The maximum rate of burning zone advance depends primarily upon the ability of the production well to produce the crude oil displaced by the in situ combustion procedure, the economics of delivering the necessary air flux density to the burning zone, and the maximum injection pressure which can be tolerated at the air injection well without exceeding the overburden breakdown pressure. Pressure disruption of the overburden would for most purposes prevent continuation of the in situ combustion procedure. It will be apparent that the problems with liquid blocks are much more emphasized at rates of burning zone advance near the maximum rate.

Usually, the liquid block, where one occurs, appears in a reservoirat a radial distance of approximately 5 feet from the ignition well during the direct combustion procedure. However, the exact distance may vary from approximately 5 feet according to the characteristics of the low-gravity, viscous crude oil and the heavy oil reservoir along with the exact conditions under which the in situ combustion procedure is carried out.

It has been proposed that the in situ combustion procedure be carried out by inverse burning, i.e., where the injection of air is countercurrent of the movement of the burning zone. All the produced crude oil must pass through the burning zone to a production well. In many cases this is undesirable since severe cracking of the crude oil can occur. Also, another disadvantage is that the amount of crude oil burned in carrying out this inverse a burning type of in situ combustion procedure is greatly increased. However, the inverse burning in situ combustion procedure possesses one great advantage. The crude oil from the heavy oil reservoir passes through a heated zone to the production well where the markedly great effect of increased temperature on the viscosity and displacement efiiciency of the thermal recovery procedure is obtained. Liquid blocks are not likely to occur under these circumstances.

It is therefore an object of the present invention to provide a secondary recovery method for recovering viscous crude oil from subterranean heavy oil reservoirs.

Another object is to produce viscous crude oil from an oil-bearing formation by direct in situ combustion without liquid blocks being formed.

Another further object is to produce viscous crude oil from heavy oil reservoirs by direct burning in situ only a small portion of the crude oil in the reservoir with the displaced crude oil passing through a heated zone to a producing well. Yet another object is to provide a direct in situ combustion procedure for recovering low-gravity, viscous crude oils from heavy oil reservoirs with a greater oil-recovering efiiciency than heretofore obtained by similar procedures.

Still another object is to provide a direct in situ combustion procedure for recovering low-gravity, viscous crude oil displaced by a burning zone advancing at near maximum rates through the heavy oil reservoir.

Another further object is to provide a method in accordance with the preceding objects where less than 15 percent of the recoverable crude oil is consumed by direct in situ combustion with the advantages of inverse in situ burning for efficiently producing the low-gravity, viscous crude oils through a heated zone to the producing well.

These and further objects will become more apparent when read in conjunction with the following detailed description of the present invention, the appended claims, and the attached drawings wherein:

FIGURE 1 is a vertical section of a heavy oil reservoir which has been subjected to certain steps of the present invention; and

FIGURE 2 is a horizontal section taken medially through FIGURE 1 with the remaining steps of the present invention applied to the heavy oil reservoir.

The objects of the present invention are achieved by a particularly effective in situ combustion method for recovering low-gravity, viscous crude oil from heavy oil reservoirs. In the method, an area of increased temperature is provided through a portion of the heavy oil reservoir to provide a heat storage region. The temperature of the heat storage region is such that a liquid block cannot develop during the advance of a subsequent direct in situ combustion burning zone therethrough at even the maximum possible rate of advance in the reservoir. The heat storage region is provided by passing a rapidly advancing burning zone between a first and second well in the reservoir. The conditions controlling the combustion are adjusted so that not more than 5 percent by volume of the crude oil in the heat storage region is consumed. Next, there is provided a third well in the heavy oil reservoir which is disposed substantially equidistant from the first and second wells. The third well 'is spaced from the nearest portion of the heat storage region not in excess of that distance at which a liquid block will occur in the heavy oil reservoir at any maintainable rate of advance of a direct in situ combustion burning zone. Subsequently, a direct in situ combustion burning zone is passed from the third well toward the first and second wells. The burning zone is advanced at a rate selected between the minimum rate of advance of the burning zone barely sutficient to maintain combustion thereof and a maximum rate of advance which is obtainable within the limitations of the ability of the first and second wells to produce oil, the economics of providing sufficient air flux density for maintaining in situ burning, and the overburden breakdown pressure. By these steps, the low-gravity, viscous oil is swept away from the third well by the effects created by the direct in situ combustion burning zone into the heat storage region. Thereafter, the crude oil moves readily before the burning zone through the heat storage region to the first and second wells due to the increased temperature therein without a liquid block occurring.

Turning now to the drawings, a detailed description of a preferred and illustrative embodiment of the present invention will be given. There is shown in FIGURE 1 a heavy oil reservoir 11 contained in the earth between an over-burden 12 and a substrata 13. For purposes of description, the overburden 12 and substrata 13 will be considered as impervious. Also, the heavy oil reservoir 11 will be assumed to contain a low-gravity, viscous crude oil having an API gravity of about 14 and a viscosity at F. of about 600 centipoises. The heavy oil reservoir 11 may be considered as being of shallow depth, comprised of poorly consolidated sand having a high crude oil saturation and a low gas saturation insufficient to provide any gas drive. The characteristics of the heavy oil reservoir 11 and the crude oil are such that the crude oil cannot be produced by utilizing natural reservoir energy. Further, it will be assumed that when the temperature of the reservoir is increased to approximately F. the viscosity of the crude oil is reduced to about 67 centipoises. This viscosity reduction is sufiicient to permit the crude oil to be recovered readily in producing oil wells.

As the first step in the present method, wells 14 and 16 are provided from the earths surface 17 through the heavy oil reservoir 11. The wells 14 and 16 may be provided with the usual well equipment, including perforated casings. The wells 14 and 16 are provided with a fiuid seal in the overburden 12, which fluid seal may comprise packer means 18 and 19. Mounted at the top of the wells 14 and 16 are wellheads 21 and 22 from which may be suspended various downwell equipment. The well 14 is provided with a perforated tubing 23. The well 16 is provided with a production tubing 24. The production tubing 24 carries on its lower extremity a suitable pumping apparatus 26 to remove formation fluids from within the well 16 to the earths surface 17 via the tubing 24. Each of the wellheads 21 and 22 carry auxiliary outlets 27 and 28 connected to the respective well annuli.

The wells 14 and 16 are spaced apart in the reservoir 11 a distance through which gas communication, as hereinafter defined, can be established. The particular distance will depend upon the formation characteristics and the means by which gas communication is to be established. For example, where air injection is the means for establishing gas communication, the wells may be 40 feet apart. Where fracturing is to be utilized as a means for establishing communication, the wells 14 and 16 are preferably more closely adjacent. Similarly, the gas communication may be established by acid leaching or treating in carbonate-containing formations.

As the next step, gas communication between the wells 14 and 16 is established. Gas communication, as the term is used herein, is a permeable channel through which air may be subsequently passed at a rate at least as great as to provide the maximum air flux density required for a burning zone moving at a maximum rate of advance therethrough. The gas communication may be established between the wells 14 and 16 by any suitable means as previously set forth. For example, air may be injected under suitable pressures through the tubing 23 in well 14 in a sufficient amount to be forced through the reservoir 11 to the well 16. A liquid hydrocarbon solvent, such as propane, may be injected into the reservoir 11 before or during air injection, if desired. Any crude oil displaced into the well 16 by the injected air may be recovered by means of the pump 26 and the production tubing 24. This method of establishing gas communication between the wells is of particular advantage in that low-temperature oxidation of the crude oil is obtained which increases the temperature in the reservoir 11. For example, most organic oxidations of crude oil evolve between 90,000 to 220,000 B.t.u.s per pound mol of oxygen contained in the air at completed reaction conditions. Stated in another manner, the heat produced may be considered to be between 50,000 and 120,000 B.t.u.s for the oxygen in 1 million standard cubic feet of air injected into the reservoir 11. If desired, a well heater (not shown) may be used in the well 14 to provide additional heat. Additionally, establishing gas communication between the wells 14 and 16 provides a highly permeable channel through which an in situ combustion burning zone may be passed at relatively high rates of advancement in the reservoir 11 without creating liquid blocking and without consuming excessive crude oil.

The next step comprises passing a rapidly advancing in situ combustion burning zone 25 from the well 14 to the well 16 so as to produce a heat storage region 29. The term heat storage region is used to denote an area in the reservoir 11 heated by the burning zone 25 to an elevated temperature not less than a certain magnitude, for example, 175 F. The temperature (i.e., a certain magnitude) of the reservoir 11 within the heat storage region 29 is increased sulficiently to prevent a liquid block from developing during passage therethrough of a subsequent direct in situ combustion burning zone at the maximum rate of advance obtainable in the reservoir 11. For example, raising the temperature of the heat storage region 29 to a temperature of not less than about 175 F. would provide a viscosity of the crude oil in the range of about 67 centipoises. This reduced viscosity would provide adequate mobility of the crude oil to prevent liquid blocking. Actually, in the present embodiment the oil mobility is increased 900 percent for the temperature increase of 75 F.

The burning zone 25 may be initiated by any suitable igniting means. Frequently, the igniting means is an electric heater (not shown) positioned in well 14. However, where the gas communicatiin between the wells 14 and 16 is established by air injection, the auto-oxidation of the crude oil may be continued until a temperature sufficient for spontaneous combustion is obtained in the reservoir 11 adjacent the well 14. This is an advantage of using air injection to esatblish gas communication. However, the present invention is not limited to this particular means for igniting the crude oil adjacent well 14 to provide the burning zone 25. The rate of air injection into tubing 23, more particularly the air flux density supplied to the burning zone 25, is controlled so that the burning zone 25 advances rapidly to well 16 without consuming not more than 5 percent by volume of the crude oil in the heat storage region 29. One means for controlling the burning zone 25 is by utilizing high injection rates for the air injected into tubing 23. This reduces the sweep efficiency of the burning zone 25 to a desired minimum. Thus, air injection occurs for a shorter period of time so that less fuel is consumed in the permeable channel formed by gas communication between the wells 14 and 16. Usually, the maximum rate of advance of the burning zone 25 of about 5 feet per day is readily obtained at high injection rates. The radial dimension of the heat storage region 29 at a certain minimum temperature is generally controlled by the amount of heat generated by the burning zone 25 passing between wells 14 and 16. If desired, an auxiliary fuel may be injected along with the air to provide the desired amount of heat. However, the area ultimately covered by the heat storage region 29 may be controlled by the amount of time in which the heat from the burning zone 25 is allowed to pass into the reservoir 11 by conduction and by convection through formation fluids. Usually,

only about 2 percent of the crude oil in the reservoir 11 within the heat storage region 29 will be consumed in providing the desired formation area of increased temperature. It will be apparent that very high rates of the burning zone 25 advance between wells 14 and 16 may be obtained through the created permeable channel between these wells. There will be no liquid blocking before this burning zone because of the existence of such permeable channel.

A third well 31 is provided as the next step of the present invention in the reservoir 11. The well 31 is disposed substantially equidistantly from the wells 14 and 16. The well 31 also is spaced from the nearest portion of the heat storage region 29 by a distance not in excess of that distance at which a liquid block occurs in the unheated reservoir 11 by a burning zone advancing between the minimum and maximum rates previously defined. Usually, the distance will be 5 feet. However, the exact distance depends upon the various characteristics of the reservoir 11 and the crude oil contained therein. The exact distance can, of course, be determined experimentally. The well 31 is provided with a suitable mechanism, like well 14, initiating a direct in situ combustion burning zone adjacent thereto in the reservoir 11 and for injecting sufficient air to move the resulting burning zone 32 toward the wells 14 and 16. The well 14 is now converted into a production well by means such as used in the well 1 5.

The crude oil in reservoir 11 adjacent the well 31 is ignited. After the crude oil has been ignited, suflicient air is introduced into the well 31 to move the direct in situ combustion burning zone 32 toward the wells 14 and 16 in heat storage region 29. The air flux density supplied to the direct in situ combustion burning zone 32 via well 31 is adjusted to insure that the burning zone 32 advances at a rate selected between the minimum rate of advance barely sufiicient to maintain combustion and the maximum rate of advance obtainable within the limitations of wells 14 and 16 ability to produce oil, the economics of providing suitable air flux density for sustaining the burning zone 32 and the overburden breakdown pressure. Generally, the rate of advance will be between 0.12 foot per day and 3.0 feet per day. Preferably, the rate of advance is maintained between 1.0 to 2.0 feet per day for best oil recovery. However, the particular rate of advance is not critical with respect to operability but is determinative of the time required to secure maximum oil recovery eficiency.

The direct in situ combustion burning zone 32 moves along stream lines 33 from well 31 to the wells 14 and 16. The burning zone 32 cannot create a liquid block inasmuch as the liquid block would have to form within the heat storage region 29. Since the heat storage region 29 is at a temperature such that no liquid block can occur, it will be obvious that large quantities of crude oil can be moved rapidly therethrough to production wells 14 and 1t: for recovery. A further advantage in passing burning zone 32 from well 31 to wells 14 and 16 is that the amount of crude oil burned to provide the heat energy required to displace the crude oil through the heat storage region 29 is relatively small compared to conventional in situ combustion procedures. One reason is that the crude oil is displaced through an area where it has greatly increased mobility. This requires a much reduced thermal drive. Thus, a given quantity of crude oil can be recovered from wells 14 and 16 with less crude oil being burned to provide the necessary thermal recovery heat energy. Usually, the amount of crude oil consumed by both burning zones 25 and 32 in the present method will be closer to 2 rather than the 15 percent by volume of the available crude oil heretofore consumed by the best thermal recovery methods.

In summary, the crude oil displaced away from well 31 by the direct in situ combustion burning zone 32 moves through the heated area of the heat storage region 29,

displacing before it, by the effects created by the burning zone 32, the more mobile crude oil contained in the heat storage region 29 into production wells 14 and 16 for recovery. Eventually, the burning zone 32 reaches the wells 14 and 16 and the method is completed. Obviously, a well 31' (the same arrangement as well 31) may be placed on the other side of heat storage region 29, to pass a burning zone 32' along stream lines 33' to wells 14 and 16 to further increase the oil recovery efficiency of the method of this invention.

It will be apparent from the foregoing that the present method effectively eliminates the problem of liquid blocks which have hampered the heretofore known in situ combustion procedures for recovering low-gravity, viscous crude oil from heavy oil reservoirs. Further, the oil recovery efficiency of the present method is greatly increased over that of the conventional in situ combustion procedures by producing the crude oil through a previously heated area without the heretofore stated inherent disadvantages.

From the foregoing it will be apparent that there has been provided herein a novel method for in situ combustion for producing a low-gravity, viscous oil from heavy oil reservoirs well suited to achieve all of the stated objects of the present invention. It is intended that the foregoing be taken as illustrative of the present invention and not limitative. Further, it will be apparent to one skilled in the art that various changes may be made to the disclosed method without departing from the spirit of the invention. It is intended that such changes be encompassed within the scope of the invention and that the only limitations to be applied are those found in the following claims.

What is claimed is:

1. A method for recovering low-gravity, viscous crude oil from heavy oil reservoirs comprising:

(a) providing first and second wells in the reservoir, said wells spaced apart a distance through which gas communication can be established,

(b) treating the reservoir after establishing gas communication between the first and second wells to create a communication zone of higher permeability to fluids than the remainder of the reservoir between the mentioned Wells,

(c) igniting the hydrocarbons in the communication zone adjacent to one of said wells,

(d) moving an in situ combustion burning zone by supplying a combustion-supporting gas to the ignited hydrocarbons between the first and second wells to provide a heat storage region surrounding the wells in which heat storage region the temperature of the reservoir is increased sufficiently to prevent a liquid block from developing during the advance of a subsequent direct in situ com-bustion burning zone therethrough,

(e) providing a third well in the reservoir disposed substantially equidistant from the first and second wells, the third well being spaced from the nearest portion of the heat storage region not in an excess of the distance in which a liquid block occurs in the unheated reservoir before a direct in situ combustion burning zone advancing therethrough,

(f) igniting the hydrocarbons in the reservoir adjacent the third well,

(g) passing a combustion-supporting gas from the third well to the first and second wells in contact with the ignited hydrocarbons for moving a direct in situ combustion burning zone from the third well to said first and second wells, and

(h) producing the crude oil displaced by the last-men- 8 tioned burning zone from the first and second wells without liquid blocking.

2. The method of claim 1 wherein the rate of the burning zone advance in step (d) is at least about 3 feet per day.

3. The method of claim 1 wherein the rate of burning zone advance in step (d) is at least about 3 feet per day and the rate of burning zone advance in step (g) is between about 1 to 2 feet per day.

4. A method for recovering low-gravity, viscous crude oil from heavy oil reservoirs comprising:

(a) providing first and second wells in the reservoir, said wells spaced apart a distance through which gas communication can be established,

(b) treating the reservoir after establishing gas communication between the first and second wells to create a communication zone of higher permeability to fluids than the remainder of the reservoir between the mentioned wells,

(c) igniting the hydrocarbons in the communication zone adg'acent to one of said wells,

(d) moving an in situ combustion burning zone by supplying a combustion-supporting gas to the ignited hydrocarbons between the first and second wells to provide a heat storage region surrounding the wells in which heat storage region the temperature of the reservoir is increased sutficiently to prevent a liquid block from developing during the advance of a subsequent direct in situ combustion burning zone therethrough,

(6) providing a third well and a fourth well in the reservoir disposed on opposite sides of a line extending between the first and second Wells and substantially equidistant from the first and second wells, the third and fourth Wells each being spaced from the nearest portion of the heat storage region not in an excess of the distance in which a liquid block occurs in the unheated reservoir before a direct in situ com-bustion burning zone advancing therethrough,

(f) igniting the hydrocarbons in the reservoir adjacent the third and fourth wells,

(g) passing a combustion-supporting gas from each of the third and fourth wells to the first and second wells in contact with the ignited hydrocarbons for moving a direct in situ combustion burning zone from each of the third and fourth wells to the first and second wells, and

(h) producing the crude oil displaced by the lastmentioned burning zones from the first and second wells without liquid blocking.

5. The method of claim 4 wherein the rate of the burning zone advance in step (d) is at least about 3 feet per day.

6. The method of claim 4 wherein the rate of burning zone advance in step (d) is at least about 3 feet per day and the rate of burning zone advance in step (g) is between about 1 to 2 feet per day.

References Cited by the Examiner UNITED STATES PATENTS 2,924,276 2/1960 Heilman et a1 16611 3,026,937 3/1962 Simm 16611 X 3,057,403 10/1962 Wyllie 16611 X 3,062,282 11/1962 Schleicher 16611 3,111,986 11/1963 Kuhn l6611 CHARLES E. OCONNELL, Primary Examiner.

BENJAMIN HERSH, Examiner. 

1. A METHOD FOR RECOVERING LOW-GRAVITY, VISCOUS CRUDE OIL FROM HEAVY OIL RESERVOIRS COMPRISING: (A) PROVIDING FIRST AND SECOND WELLS IN THE RESERVOIR, SAID WELLS SPACED APART A DISTANCE THROUGH WHICH GAS COMMUNICATION CAN BE ESTABLISHED, (B) TREATING THE RESERVOIR AFTER ESTABLISHING GAS COMMUNICATION BETWEEN THE FIRST AND SECOND WELLS TO CREATE A COMMUNICATION ZONE OF HIGHER PERMEABILITY TO FLUIDS THAN THE REMAINDER OF THE RESERVOIR BETWEEN THE MENTIONED WELLS, (C) IGNITING THE HYDROCARBONS IN THE COMMUNICATION ZONE ADJACENT TO ONE OF SAID WELLS, (D) MOVING AN IN SITU COMBUSTION BURNING ZONE BY SUPPLYING A COMBUSTION-SUPPORTING GAS TO THE IGNITED HYDROCARBONS BETWEEN THE FIRST AND SECOND WELLS TO PROVIDE A HEAT STORAGE REGION SURROUNDING THE WELLS IN WHICH HEAT STORAGE REGION THE TEMPERATURE OF THE RESERVOIR IS INCREASED SUFFICIENTLY TO PREVENT A LIQUID BLOCK FROM DEVELOPING DURING THE ADVANCE OF A SUBSEQUENT DIRECT IN SITU COMBUSTION BURNING ZONE THERETHROUGH, (E) PROVIDING A THIRD WELL IN THE RESERVOIR DISPOSED SUBSTANTIALLY EQUIDISTANT FROM THE FIRST AND SECOND WELLS, THE THIRD WELL BEING SPACED FROM THE NEAREST PORTION OF THE HEAT STORAGE REGION NOT IN AN EXCESS OF THE DISTANCE IN WHICH A LIQUID BLOCK OCCURS IN THE UNHEATED RESERVOIR BEFORE A DIRECT IN SITU COMBUSTION BURNING ZONE ADVANCING THERETHROUGH, (F) IGNITING THE HYDROCARBONS IN THE RESERVOIR ADJACENT THE THIRD WELL, (G) PASSING A COMBUSTION-SUPPORTING GAS FROM THE THIRD WELL TO THE FIRST AND SECOND WELLS IN CONTACT WITH THE IGNITED HYDROCARBONS FOR MOVING A DIRECT IN SITU COMBUSTION BURNING ZONE FROM THE THIRD WELL TO SAID FIRST AND SECOND WELLS, AND (H) PRODUCING THE CRUDE OIL DISPLACED BY THE LAST-MENTIONED BURNING ZONE FROM THE FIRST AND SECOND WELLS WITHOUT LIQUID BLOCKING. 